First understand filter basics
The minimum efficiency reporting value (MERV) of filters range between 1 and 16. The residential air filter that you use falls between 4 to 12.

They are mostly made of spun fiberglass in order to filter out smaller micron particles, protect the furnace and provide maximum airflow. Keep in mind 25 percent of particles in the air inside your home are in the 3 to 10 micron range. Most residential filters therefore, come in 4 to 12 range.

How much you need to spend?
How much you want to spend is up to you. But before you decide what residential air filter to buy consider this. More expensive filters have been identified by many as having smaller effect on indoor air quality. Most expensive filters restrict air flow as they get dirty and that could lead to premature failure of your furnace. If the heat exchange gets too restricted, the furnace is equipped to shut down itself.

For most homeowners, MERV 7 or 8 would provide a good balance and good purchase. Remember to look for a pleated filter. It could trap 80 to 95 percent of the particles that are 5 microns or larger.

What are you trying to filter?
As we mentioned above, you need to aim to eliminate particles that are 5 microns or larger and choose a replacement furnace filter that can capture up to 95 percent of those particles. Never reuse a filter by washing or vacuuming it after it gets dirty.

How often should you change your furnace filters?
The answer is somewhat complicated. Many experts used to say that you should inspect your furnace filter every month. At the time this recommendation came into play, we were using inch-thick fiberglass pads and there were so much space between fibers.

They were only effective at blocking larger particles that could harm the furnace, not much effect on your health. Today filters are much more advanced than those were used in the past. New technology allow more filter surface area due to their zigzag design, remove up to 90 percent of mold spores and pet dander(a claim made by 3M), and effective in attracting 3 to 10 microns including bacteria that are much smaller than human hair (20 to 40 microns). Look at the collection at Your Filter Connection.

Many manufacturers now recommend that you replace your furnace filters every three months. However, your monthly inspection will give you an idea whether you need to change your filters sooner. At a minimum you should change your filters every season because we go from air conditioning to heating when seasons change.

You can find a wider selection of filters at Your Filter Connection.